X-ray tube



6 1 626,465 April 26, 1927. G. HOLST ET AL X-RAY TUBE Fi1edNov.6. 192s 2 Sheets-Sheet 1 5 April 26, 1927.

G. HOLST ET AL X-RAY TUBE Filed Nov. 6, 1923 mm cilIlll fllllmllll:

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22 W WWW 49W Patented Apr. 2%, 1927.

/ ttZtAt-S GILLES HOLST AND ALBERT BOUWERS, OF EINDHOVEN, NETHERLANDS, ASSIGhlOBS TO NAAMLOOZE. VENNOOTSCEAP PHILIPS HOVEN, NETHERLANDS.

1 X-BAY GLoEI-LIAMPENEABRIEKEN, or amn- TUBE. i

Application filed November 6, 1923, Serial No. 873,166, and in the Netherlands December 8, 1922.

This invention relates to X-ray tubes having a glow-cathode arranged within an evacuated envelope and also to a device for operating such tubes.

Accordin to the pre sent invention the glow-catho .e of Xray tubes is disposed within a metal vessel, at least a part of the wall of said vessel forming part of v the envelope of the 'X-ray tube, and the the metal vessel may be constricted on that side adjacent the anticathode to form an aperture for the passage ofi the cathode rays, and that portion of the surface of the "anticathode to be struck by the cathode rays is located in or adjacent the said aperture.

In an X-ray" tube according to the invention the glow-cathode is also preferably insulated from the metal vessel.

In the arrangement according to the in- -vention for operating the improved X-ray tube, the metal vessel in which the glowcathode is disposed, is connected to the glow-cathode preferably conductingly or via a source of'constant but regulable voltage. It is particularly advisable that the glow-cathode and the metalvessel are-connected in such a manner by a resistance or a source of voltage that the metal vessel has a constant negative potential difference relative to all points of the filament.

It has already been proposed tomake high vacuum X-ray tubes in which the greater part of the envelope is of metal. In these known tubes, however, the anticathode forms part of the'said metal portion or is at least conductingly connected thereto, whereas in contradistinction to this the tube according to the present invention has the anticathode insulated from the metal part of the tube so as to allow of a great potential difference between the anticathode and the said part.

The known X-ray tubes with a metal envelo e as compared with those having an enve ope of glass have various advantages for example less fragility ,and the X-rays being better reproducible owing to the charge of the glass wall being no longer harmful. The present invention has the aforesaid ad'- vantages, the improved reproduction being -ray tube according to the effected by giving a constant potential to the metal part. Moreover, the focussing devlce forthe X-rays may be dispensed with. The cathode rays emitted by the glowcathode need not be converged to a beam, but the metal vessel and the anticathode may be so shaped and arranged relative to each other that the cathode rays can strike only a limited area of the anticathode.

Incidental to this is the advantage that there is greater liberty in regard to the construction and the arrangement of the filament. The area of the anticathode struck by the cathode rays may be easily adjusted.

According to the present vinvention the metal vessel and the anticathode may preferably be so shaped and arranged relatively to each other that the active X-rays are directed at an angle, preferably at right angles to the surface of the anticathode.

According to the invention a very simple and advantageous construction is ensured by the coaxial arrangement of that portion of the anticathode to be struck by the cathode rays, the aperture in the metal vessel for the passage of the cathode rays and the' aperture or the window in the said vessel for the passage of the X-rays.

In this construction the fact that the incandescent cathode need no longer be arranged in a concentrated shape is taken advantage of. It may for example be disposed annularly around the axis of the parts which are coaxially arranged, it being thus X-rays to' leave the tube possible for the undisturbed.

The accompanying drawings represent by way of example some constructions of X- ray tubes embodying the invention. In the said drawings F1gure 1 1s an X-ra prlnciple of the nventlon is shown.

Figures 2, 3, 4 and 5 show some embodi- I ments adapted for practical use.

tube in which the.

Figures 4 and 5. show in addition to the X-ray tube a part of the device necessary for tgperating it.

In the' ray tube illustrated in. Figure 1 the glow-cathode 1 is enclosed within a metal vessel 3 in which the anticathode 2 is also enclosed. The conductors for the glow-cathode are sealed in a glass tube 4 which is hermetically fused to the vessel 3. The anticathode 2 is insulated from the metal vessel by an insulating member 5 which is preferably of glass and likewise hermetically sealed to the metal vessel.

The tube is exhausted in any known manner to a very low pressure (for example lower than 0.0006 millimeters of mercury).

In operating the tube illustrated in Flgure 1 a high voltage is maintained between the glow-cathode 1 and the anticathode2, and the metal vessel 3 is kept at a constant potential relative to the glow-catho de. This may be ensured for example by conductingly connecting one end of the glow-cathode to the metal vessel. The glow-cathode may-also be connected to the metal vessel via a source of constant voltage. In doing so care shoul be taken that the metal vessel 3 is given a negative potential in relation to all points If this negative potential of the electrons emitted by the glow-cathode will be capable of striking the wall'of the metal vessel but all'of them will be forced to pass to the anticathode 2. In the drawing the latter is shaped as a small spherical body so that the cathode rays can only strike a small area of the anticathode, the X-rays.

being thus emitted by a small surface, as is known'to be necessary for makingradio- The metal Vessel 3 should be rovided at some suitable oint with a win ow for the passage of the -rays.

The potential difference between the metal vessel 3 and the glow-cathode may also be slightly positive, but this has the detrimental effect that part of. the electrons emitted by the glow-cathode will strike the metal.

ing of the metal wall.

The embodiment of'the invention according to Figure 1 isnotwell adapted for practical use, as the anticathode 2 cannot be sufficiently cooled. I r

An embodiment of-theinvention which is more adapted for practical use is illustrated in Figure 2. The glow-cathode-9 which is a circular filament is disposedwithin a metal vessel 6 which at 7 is constricted to form a small aperture in which part of the anticathode 8 is located. Opposite said anticathode the metal vessel is provided with a window 13, 14 for the passage of the X-rays generated. The window illustrated coinwall which causes loss of energy and heat-- prises a glass plate 13, hermetically sealed to the metal wall and a thin metal plate 14 of for instance aluminum or silver, or in lieu thereof a grid or gauze of similar material may be provided which is transparent to X-rays but prevents the glass plate fromv becoming charged by the cathode rays.

The thin metal plate or grid 14 is provided with the object of making the vessel contain ing the glow-cathode as far as possible of metal throughout. Ifa small negative potential difference is brought about between the metal vessel and the glow-cathode no electrons emitted by the glow-cathode will be capable of reaching the wall of the vessel and consequently of injuring the regular functioning of the tube. The conductors 10 and 11 for the glow-cathode are sealed in a glass tube 12, which is hermetically fused to the metal vessel. The filament 9 which consists for example of tungsten, is supported by short legs 16, of for examplemolybdenum, which in turn are secured to a ring 15 of suitable insulating material, for example glassv or porcelain. The anticathode is insulated from the metal vessel by an insulation capable of resisting any high tension.

area of the anticathode owing to the particular shape of'the metal vessel and to the arrangement of the anticathode relatively v to said vessel,

The anticathode may be cooled in any suitable manner.

As regards the potential difference between the glow-cathode and the metal vessel the" same conditions are to be observed as before mentioned with regard to Figure 1..

If the glow-cathode comprises a tungsten filament a negative potential difference of say'5 volts, is sufiicient to prevent the electrons emitted by the glow-cathode from striking the metal wall.

It may be observed that it is not absolutely necessary to'insu'late both conductors for the glow-cathode, from the metal vessel. One of the conductors may also be directly connected, conductingly -'or via a' resistance, to themetal vessel, the other conductor only being insulated and introduced into the tube.-

This has, however, the disadvantage that the potential. difference between the glowcathode and the metal vessel is not regulable.

III!) In the construction according to Figure 3 v the anticathode and the metal vessel are shaped and arranged relatively toeach other fina somewhat different way. To the wall of the metal vessel 21 a metal cover or parti-- cathode. By regulating the tension of the metal vessel in relation to the glow-cathode and consequently in relation to the anticathode .the area of the anticathode struck by the cathode rays can be somewhat varied.

In the construction according to Figure 4 the metal vessel 23 is provided with a slanting metal plate 24, in which is an aperture 33. Opposite this aperture is the anticathode 25, insulated from the metal vessel by the insulating material 27. The X-rays generated are projected through a window 26 which is constructedin a manner similarto that illustrated in Figure 2.

.The glow-cathode 28 is insulated from the only 'through this aperture thus ensuring that only a small area of the anticathode is used for generating -X-rays.

The anticathode may consist of any suit able material such-for example as.molybdenum, tungsten.

In the construction according to Figure 5, which largely corresponds to that of Figure ,4, the insulating support 27 for antia cathode 37 being broken away, the filament '38 and the window 39 are arranged relative to the anticathode 37 in the same manner as shown in Figure 2.

' The arrangement of electrical circuits for operating the X-ray tubeshown in Fig 5 corresponds to'that shown in Fig. 4 corresponding reference numbers referring to corresponding parts.

As regards operating the X-ray tube it may be observed that although it is sufficient to supply a small negative voltage to the metal vesselwhich is. low in relation to that supplied to the cathode, said voltage may also be chosen somewhat higher which does not materially injure the functioning of the tube.

As material for the metal vessel, co per or iron for example may be used and or hermetically sealing the metal vessel to the glass parts of the envelope a platinum 'ring may be used; For this latter purpose a chrome-iron ring maybe used to advantage if the'chrome-irorl is so composed that lts 7 thermal coeflicient of expansion is substanmay be deprived of the occluded gases and its minute porosity are particularly useful properties.

What we claim is:

1. An X-ray tube comprising a cathode within ahigh vacuum vessel, said vessel consisting partly of metallic material and forming a part of the envelope of the tube, an anticathode insulatedfrom said vessel by an insulation capable of resisting the operating voltage between the cathode and the anticathode, the metal vessel having a portion adjacent the anticathode so shaped and arranged relativelyto the anticathode that the cathode-rays are caused to strike only a limited surface of the anticathode.

' 2. An X-ray tube comprising a cathode within a high vacuum vessel, said vessel consisting partly of'metallic material and forming a partof the envelope of the tube, ananticat ode insulated from said vessel by an insulation capable of resisting the operating voltage between the cathode and the anti cathode, the metal vessel on the side adja cent the anticathode being constructed to form. an aperture for the passage of the cathode rays, the portion of the surface oi the anticathode to be struck by the cathode rays being located adjacent said' aperture.

3. An X-ray tube comprising an incandescent cathode within a high vacuum vessel consisting partly of metallic material and forming a part of the envelope of the tube, an anticathode insulated from said vessel by an insulation capable of resisting the operating voltage between the incandescent cathode and the anticathode, the

metal vessel having a portion adjacent the anti-cathode so shaped and arranged relatively to the anticathode that the cathode rays are caused to strike only a limited surface of the anticathode, one end of the fila-. ment and the metal vessel being connected conductively.

4.-An X-ray tube comprising an incandescent cafhode within a hlgh vacuum vessel COHSISlZIIIg partly 0t metallic material and forming a part of the envelope of the .metal vessel on the side adjacent the anticatho e being constricted to form an aperture for the passage of the cathode rays,

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the portion of the surface of the anticathode to be' struck by the, cathode rays being 10- cated adjacent said aperture, one end of the filament and the metal vessel being connected conductively.

5. An X-ray tube comprising an incandescent cathode within a high vacuum vessel, said vessel consisting partly of metallic material and forming a part of the envelope of the tube, an anticathode insulated from said vessel by an insulation capable of resisting the operating voltage between the incandescent cathode and the anticathode, the

, metal vessel having a portion adjacent the lope of the tube, an anticathode insulated from said vessel by an insulation capable of resisting the operating voltage between the "incandescent cathode and the anticathode,

the'metal vessel on the side adjacent the anticathode being constricted to form an aperture for the passage of the cathode rays, the portion of the surface of the anticathode to be struck by the cathode rays being located adjacent saidaperture, one end of the filament and the metal vessel-being connected :by a resistance.

7. An X-ray tube comprising an incandescent cathode within a hlgh vacuum vessel,

said vessel consisting partly of metallic material and forming a part of the envelope of the tube, an anticathode'insulated from said "esscl by an insulation capable of resisting the operating voltage between the incandescent cathode and the anticathode, the metal vessel having a portion adjacent the anticathode so shaped and arranged relatively to the anticathode that the cathode rays are caused to strike only a limited surface of the anticathode, and a source of voltage inserted between the metal vessel and one end of the filament.

- 8. An X-lflY] tube comprising an incandescent cathode within a high vacuum vessel, said vessel consisting partly of metallic material and forming apart of the envelope of the tube, an anticathode insulatedfrom said vessel by an insulation capable of resisting the operating voltage between the in-.

candescent cathode and the anticathode, the

metal vessel on the side adjacent the anticathode being constricted to form an aper-' ture for the passage of the cathode rays, the portion of the surface of the anticathode to be struck by the cathode rays being located adjacent said aperture, and a source of volt age inserted between the metalvessel andone end of the filament. 9. An Xray tube comprising a cathode and an anti-cathode spaced therefrom, a

metallic member surrounding the space hetween the two electrodes and forming a part of the wall of the tube, and means to maintain and regulate a potential difference be tween said cathode and'said metallic member whereby the area of the anticathode struck by the cathode rays is controlled.

10. An X-ray tube comprising a vacuum vessel, a cathode and an anticathode mounted in spaced relation within said vessel, a

metallic member surrounding the space between the electrodes and forming a part of the wall of said vessel, and means to maintain a difference of potentialbetween said member and said cathode.

cathode mounted in spaced relation within said vessel, a. metallic member surrounding the space between said electrodes andforming a part ofthewall of said vessel, a

circuit for heating said cathodeincluding a resistance, andan electric path connecting" resistance.

In testimony whereof we tures.

-GILLES HOLST. ALBERT BOUWER S.

said member and said cathode including said aflix our signa- 

